The present invention generally relates to double-sided milling inserts, and more particularly to a double-sided milling insert suitable for use in a high feed milling holder forming a high feed milling tool and a method of high feed milling.
In milling operations, a method of cutting a workpiece by increasing i.a. feed rate (feed distance per tooth) of a milling tool is called high feed milling. High feed milling is a milling method that permits faster machining than other milling methods. It pairs shallow depth of cut, such as 2 mm or less, with high feed per tooth or cutting edge which gives higher metal removal rates, resulting in more parts being machined. Cutting forces are directed along the axis of the machine spindle which means greater stability and reduced vibrations, thereby extending tool life. The method takes advantage of small setting angles. This gives minimal radial cutting forces and maximum axial cutting forces, which stabilizes machining and reduces the risk for vibrations. In turn, this allows raised parameters for cutting even when machining with a large overhang.
The milling tool mounted on the milling machine conventionally comprises several milling inserts mounted at the periphery of the milling tool so that each active cutting edge is oriented substantially radially in the milling tool.
Trigon style cutting inserts are frequently used with cutting edges designed with big radii, especially in vertical or plunging operations trigon style inserts offer good chip evacuation. Cutting inserts used have a substantially triangular profile, each intended to be positioned substantially in a plane of the axis of rotation of the milling cutter body. It is common to provide a straight cutting edge in contact with the surface to be machined. However the arrangement of such a cutting edge may require more power during machining and lead to tolerance sensitivity, vibrations and/or impaired chip removal rate.
EP 2703108 A1 discloses a milling tool having trigonal milling insert mounted therein.
Changes in the configuration of the cutting insert have been proposed so as to have angled clearance surfaces to allow for an optimized orientation of the cutting edge of the cutting insert mounted in the milling cutter body and relative to the material surface to be machined. However, even if such geometries may allow an improved function of the cutting operation, the production of these cutting inserts requires complex steps of pressing and machining that generate costs and production times can be extended.
The present invention is intended to overcome these drawbacks by proposing a high feed milling insert and a high feed milling tool adapted to be easily produced at a relatively low cost while maintaining the quality of cutting.
It is desirable to provide a double-sided milling insert that can be mounted on a toolholder at a favorable radial angle. It is further desirable to provide an insert that can be well supported by the toolholder.
It is desirable to provide a double-sided milling insert and a high feed milling tool which provide improved performance and which are suited for applications in which commonly round-shaped cutting inserts are used and high-feed surface finishing applications.
In accordance with an aspect of the invention, a double-sided milling insert for high feed milling of metal workpieces wherein the insert has a trigonal basic shape and comprises upper and lower faces facing in opposite directions and convex clearance surfaces extending between the upper and lower faces, each one of the faces comprising a recessed support surface, said support surface being substantially parallel to the other support surface, and having a cavity therein for receiving a fastening means, intersections of the convex clearance surfaces with the upper and lower faces forming convex cutting edges when seen in a plan view, a rake face being provided adjacent the convex cutting edges, wherein each convex cutting edge is concave when seen in a side view, each convex cutting edge comprises a substantially straight cutting edge portion on each side of a curved cutting edge portion when seen in a plan view. Each cutting edge has a first straight cutting edge portion and a second straight cutting edge portion on each side of the curved portion, wherein the first straight cutting edge portion and the second straight cutting edge portion each follows a straight or convex path in a side view and are both straight in a plan view. The curved portion has a length that is longer than the length of anyone of the straight cutting edge portions. The curved cutting edge portion facilitates formation of a curved wiper edge to achieve fine surface finish in the metallic workpiece and facilitates determination of the setting angle.
In accordance with another aspect of the invention, adjacent clearance surfaces meet at a first corner defining a bisector, wherein said clearance surfaces form an obtuse corner angle. A tangent to a convex cutting edge forms an internal acute angle with a plane containing the clearance surface at the corner when seen in a side view. The clearance surface comprises a substantially planar portion at each side of a central curved portion of the clearance surface making tool holder pocket easier to manufacture.
In accordance with another aspect of the invention, each convex clearance surface comprises a waist in the area of the central curved portion when seen in a side view, which is advantageous for reducing power requirements.
In accordance with another aspect of the invention, the obtuse corner angle is in the range of 95 to 120° which is advantageous for strength and for copy milling.
In accordance with another aspect of the invention, the bisector lies in a bisector plane which intersects the waist which is advantageous for maximizing the support surface area on the insert.
In accordance with another aspect of the invention, the bisector plane intersects a center or center line of the cavity which is advantageous for achieving a symmetrical insert.
In accordance with another aspect of the invention, lowest points of curved portions of the cutting edges are located at opposite sides of the bisector plane which is advantageous for reducing power requirements.
In accordance with another aspect of the invention, each convex clearance surface is perpendicular to a plane parallel to a recessed support surface thereby providing durable negative basic insert geometry.
In accordance with another aspect of the invention, the convex cutting edge is substantially V-shaped when seen in a side view, wherein a line intersecting the lowest point of the convex cutting edge and a highest point of the corner forms an angle with a plane P1 that is in the range of 5 to 15°. A V-shaped cutting edge brings a relatively smooth cut entry at milling.
In accordance with another aspect of the invention, a rake face is directly or indirectly connected to the convex cutting edge, wherein the rake face forms a positive rake angle gamma which is an additional measure for reducing power requirements.
In accordance with another aspect of the invention, the rake face is partially connected to the convex cutting edge via a chamfer forming a negative angle with the plane to strengthen the cutting edge.
In accordance with another aspect of the invention, the rake face is located on a circumferential ledge extending above the support surface to distance the support surface from the region of chip flow and thus facilitate chip removal.
In accordance with another aspect of the invention, the rake face extends higher above the support surface at the corners than at the central curved cutting edge portion to avoid disadvantageous material accumulation occurring by so called smear-on.
In accordance with another aspect of the invention a high feed milling tool is disclosed having a longitudinal axis of rotation and comprising a tool body having a plurality of insert pockets formed in a front end of the tool body and a plurality of double-sided milling inserts retained in the plurality of insert pockets, each insert pocket comprising a pocket bottom abutment surface, a threaded hole extending tangentially rearwardly from the pocket bottom abutment surface, pocket side walls extending upwardly from the pocket bottom abutment surface, two of the pocket side walls being pocket abutment surfaces that form a pocket internal obtuse angle with the pocket bottom abutment surface, wherein the pocket bottom abutment surface is raised relative to its closest surrounding, and wherein each side of the pocket bottom abutment surface comprises a substantially straight portion on each side of a central curved portion to provide a correct indexing of the cutting insert. At least one milling insert is mounted in an insert pocket at a setting angle in the range of 5 to 15°.
In accordance with another aspect of the invention a method of high feed milling of a metallic workpiece is disclosed comprising the steps of providing a high feed milling tool of the above-captioned type in a milling machine, arranging milling inserts at a setting angle in the range of 5 to 15°, operating at 800 to 1300 rpm, at up to about 2 mm in depth-of-cut, and at a feed rate of 5 to 10 meters per minute.